Mar. 15, 1924 
Studies on the Potato Tuber 
831 
is very gradual. The transition cells are oblong or pointed (PL 10, G, 
and fig. 8). 
Hebron. —Periderm normally thick, smooth, or covered with a thin 
rough crust. Layer measures 143 microns and is composed of 8-9 rows 
of cells. The rows are usually broad, but the uniformity is broken in 
Fig. 7. —Semidiagrammatic drawings of periderm of potato tubers. X40. 
that narrow rows are often interpolated between wide rows. The larger 
cells measure, 137 by 14.8 microns, on the average. A narrow but gradual 
transition zone connects the periderm with the cortex. The cells of the 
transition zone are rectangular; as they approach the cortex they become 
oblong or polyhedral (PL 10, H, and fig. 8). 
